Field of the Invention
The present invention relates to an image pickup apparatus and a radiation image pickup system.
Description of the Related Art
As discussed in Japanese Patent Application Laid-Open No. 2002-344809, there is a radiation image pickup apparatus including a holding unit (a sample and hold circuit) that holds a signal indicating the amount of radiation used to irradiate each pixel of a sensor array (hereinafter, referred to as “signal S”). As discussed in Japanese Patent Application Laid-Open No. 2002-344809, the signal S indicating the radiation amount can be individually held by a first holding unit via an amplification unit in each pixel. Therefore, reading a signal from one frame and performing radiation exposure for the next frame can be performed simultaneously. Further, according to Japanese Patent Application Laid-Open No. 2002-344809, a second holding unit is provided to hold a signal representing a noise component (e.g., offset) generated by the amplification unit (hereinafter, referred to as “noise signal SN”). Further, according to Japanese Patent Application Laid-Open No. 2002-344809, it is possible to perform processing for reducing the noise component from the signal S held by the first holding unit (e.g. correlated double sampling (CDS) processing).
On the other hand, as discussed in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-525983, there is a conventional image pickup apparatus that acquires signals, for example, at two sensitivity levels (hereinafter, referred to as signals S1 and S2) in each pixel and generates image data using these signals S1 and S2. According to the technique discussed in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-525983, two holding units are provided in each pixel so that the signals S1 and S2 obtained at respective sensitivity levels can be held in respective holding units and can be individually read.
However, in each of Japanese Patent Application Laid-Open No. 2002-344809 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-525983, it may be difficult to sufficiently reduce a noise signal N from the signal S of each pixel. In each of Japanese Patent Application Laid-Open No. 2002-344809 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-525983, each pixel has a complicated configuration. Therefore, the influence of heat generated by the amplification unit imparted on each holding unit will be variable depending on an internal layout of the pixel. The noise component influencing the signal component held by each holding unit will be differentiated. The noise component is variable depending on the temperature. Therefore, in such a case, there is a difference between the noise component included in the signal S and the noise component included in the noise signal SN, and thus it may be difficult to sufficiently reduce the noise component from the signal S.